

It is incredibly annoying when you are transferring data between two devices. Whenever these kinds of problems occur, your external hard drive doesn't show on your Mac.

If your external drive connected through a wall outlet, use a different wall outlet.A USB port( Thunderbolt port) is damaged, it might be a hardware problem of your Mac, so try a different port.Data cable is damaged or exposed( try different cable).I evaluated some possible cusses that are going to mention below. If you connected your external hard drive with your Mac, and it's not responding like discussed above, definitely there is a kind of particular problem behind the scene, that you didn't recognize yet. Why does my external hard drive keep disconnecting? Change the format of your external hard drive

Recover or backup your drive data before format Check if your Mac can recognize the external hard drive Why does my external hard drive keep disconnecting?.
